†RNA-like Structures in the Genomes of RNA Viruses

Abstract

All structural studies of ribonucleic acids (RNAs) from various origins—be they cellular messenger RNAs or viral RNAs—show that these molecules contain nucleotide sequences that are not translated into polypeptides. At the 5' end, besides the “cap” structure generally found in eukaryotic mRNAs and viral RNAs, the untranslated sequence is heteropolymeric and of variable length—from a few nucleotides to a few hundred nucleotides. The physiological role of these untranslated heteropolymeric regions is not well understood. This chapter summarizes the results obtained with different viral RNAs that accept an amino acid and are recognized by various tRNA-specific enzymes. For a number of these viral RNAs, the nucleotide sequence of the amino-acid-acceptor regions has been determined and the structures have been compared. Results indicated that different primary and secondary structures of two nucleic acid molecules, such as tRNAs and certain viral RNAs, can be recognized efficiently by the same enzyme systems that play a central role in the transfer of genetic information. The nucleotide sequence of virtually all tRNA molecules can be drawn in a hydrogen-bonded “cloverleaf” structure. The existence of this structure, further folded into a tertiary structure, has been proved by X-ray diffraction analyses. The chapter concludes with a discussion on the possible role of tRNA-like structures in viral RNA genomes.